1. Brief Description of the Invention
The invention described herein involves improved thickening compositions often referred to as Theological additives, viscosity modifiers or thixotropes, used to impart rheological and viscosity modification properties to a wide range of oil and organic based systems used as paints and coatings. In many commercial applications, such a thickening Theological chemical is added to an oil or organic based paint or coating system, for example epoxy paint, to change or modify the rheological properties of the system. The invention also includes paints and coatings containing such additives.
In an important aspect the invention covers a Theological additive consisting of the reaction product of:
a) a diamine selected from the group consisting of ethylene diamine and hexamethylene diamine;
b) one or more straight chain monocarboxylic acids having 4 to 8 carbon atoms; and
c) 12-hydroxystearic acid.
The invention is based on a discovery that certain castor based rheological additives, while imparting desirable rheology, impair recoatability and intercoat adhesion of the system in which they are utilized where such systems, after drying, is painted or coated over with a second paint or coating composition. The present invention shows that these undesirable side effects can be avoided by using the inventive additives.
Normally Theological additives should show no reactivity, so they do not react with any other ingredients in the systems in which they are used. Intercoat adhesion is defined as adhesion between adjacent layers of paint when more than one coat of paint or coating is applied to a substrate. Examples of such use are primer and topcoats in home painting and a series of paint coatings applied to automobiles and appliances.
We have concluded it is essential when using additives to structure their chemistry so that, at necessary dosage, they do not adversely affect paint and coating compositions used by customers in systems where more than one coat will be applied to a substrate.
2. Description of the Prior Art
It has been known in the art for many years to use various materials as rheological additives to, among other Theological properties, modify the viscosity of organic systems. Such systems can include paints and coatings, inks, construction materials and wood stains. Depending on the composition of the system, the products made with these thickeners are preferably useful as coatings and paints.
The present invention includes novel rheological additives as well as organic fluid composition containing such additives.
Rheology is defined as the science of the flow and deformation of matter. Rheological additives can be defined as substances added to liquid systems which change that system""s flow and viscosity properties. Proper rheology for storage and application must be balanced with the requirement of many fluid systems to resist sagging and dripping during and following application. The term xe2x80x9cthixotropyxe2x80x9d describes a type of flow behavior in which a temporary reduction in a fluid""s viscosity by the application of shear, such as through the use of a paintbrush or atomizing equipment; once the shear forces have been removed, such as following deposition of the liquid onto a surface), the system will regain its initial, higher viscosity.
For background, Japanese Patent Application No. 62-69957 describes a sag preventor for non-aqueous coating materials comprising a mixture of two different fatty acid amides wherein fatty acid amide (A) is obtained by reacting a mixture of at least one straight chain saturated fatty acid having 3-4 carbon atoms and 12-hydroxystearic acid (the molar ratio of the fatty acid and 12-hydroxystearic acid being 1:9-8:1) and ethylene diamine or hexamethylene diamine and fatty acid amide (B) is obtained by reacting a mixture of at least one straight chain saturated fatty acid having 6-22 carbon atoms and 12-hydroxystearic acid (the molar ratio of the fatty acid and 12-hydroxystearic acid being 0:10-8:2) and ethylene diamine, hexamethylene diamine, or xylyiene diamine wherein the weight ratio of fatty acid amide (A) to fatty acid amide (B) is 100:00-20:80.
Products believed to be the reaction product of ethylene diamine, a monocarboxylic acid having ten carbon atoms and 12-hydroxystearic acid have been sold for many years as Theological additives. A product, designated comparative X, using this chemistry has been used as a comparative example to the invention hereof in the below following examples.
It is an object of the present invention to solve or substantially alleviate the problems created by prior art thickeners in thickening compositions for organic systems. It is, therefore, a more specific object of the present invention to an additive which will provide paints and coatings without affecting intercoat adhesion.
This invention provides amide compositions having at least two amide moieties per molecule which comprises reacting preferably by known condensation reactions, a diamine selected from ethylene diamine, hexamethylene and mixtures thereof diamine and mixtures thereof, one or more monocarboxylic acid of the formula:
R1xe2x80x94COOH
wherein R1 is a straight chain saturated aliphatic hydrocarbon radical of 3 to 7 carbon atoms and 12-hydroxystearic acid. The inventors have found that the inventive composition provides improved rheological and suspension properties to non-aqueous coating systems and more importantly the inventive composition does not cause intercoat adhesion failures of topcoats subsequently applied to primers.
In an important aspect the invention covers a rheological additive consisting of the reaction product of:
a) a diamine selected from the group consisting of ethylene diamine and hexamethylene diamine;
b) one or more straight chain monocarboxylic acids having 3 to 7 carbon atoms in the straight chain saturated aliphatic hydrocarbon radical; and
c) 12-hydroxystearic acid.
The invention preferably relates to a composition, which is obtained by reacting
a) 2 equivalents of a chemical selected from ethylene diamine, hexamethylene diamine and mixtures thereof;
b) from 0.4 to 1.8 equivalents of a straight chain monocarboxylic acid having 3 to 7 carbon atoms in the straight chain saturated aliphatic hydrocarbon radical; and
c) from 1.6 to 0.2 equivalents of 12-hydroxystearic acid, such that no essentially free acid and amine is left unreacted at the end of the condensation reaction.
A most preferably aspect of this invention relates to a rheological additive composition consisting of a reaction product of:
1) ethylene diamine;
2) one or more straight chain monocarboxylic acids having 3-7 carbon atoms in the straight chain saturated aliphatic hydrocarbon radical; and
3) 12-hydroxystearic acid.
wherein the equivalent ratio of monocarboxylic acid and 12-hydroxystearic acid is 0.4:1.6 to 1.8:0.2 and there are 2 equivalents of ethylene diamine.
The term xe2x80x9cequivalent(s)xe2x80x9d is used and is intended to have its standard meaning as employed in the art (see for example Hawley""s Condensed Chemical Dictionary 1987, 11th Edition). However, for additional clarity, equivalents refer to the number of reactive groups present in a molar quantity of a molecule, such that a mole of a diamine (e.g. ethylene diamine) has two equivalents of amine and a mole of 12-hydroxystearic acid has one equivalent of carboxylic acid. Furthermore a monoacid has only one reactive group and a diamine has only two reactive groups (preferably both primary amines), and a monocarboxylic acid has one carboxylic acid group and these are preferable, although not necessarily, the only reactive materials present in the reaction mixture.
The diamines of component a) useful for the present invention include ethylene diamine and hexamethylene diamine with the most preferred being ethylene diamine. Hexamethylene diamine is often referred to as hexane diamine. These are common chemicals and can be obtained from a large number of chemical manufacturers.
The chemicals useful for component b) include monocarboxylic acids of the formula R1xe2x80x94COOH where R1 is between 3 and 7. Such acids are commercially available and include butyric acid, pentanoic acid, hexanoic acid, heptanoic acid and octanoic acid. The monocarboxylic acid of the formula R1xe2x80x94COOH wherein R1 is C8 and above falls outside the preferred acids. A preferred acid is heptanoic acid with the most preferred hexanoic acid. These acids are commercially available for example from Acme Hardesty Company, Penta Manufacturing Company and Procter and Gamble Company and others.
Component (c) is 12-hydroxystearic acid. This acid is produced from hydrogenated castor oil and is a straight C18 carbon chain saturated fatty acid with an OH group attached to the 12th carbon atom. Suppliers of such products include, for example, CASCHEM, Inc and Acme-Hardesty Company.
Generally the Theological additives of the present invention are preferably prepared according to known condensation reaction. The diamine, monocarboxylic acid and 12-hydroxystearic acid are reacted together in stoichiometric amounts so that no excess of the acid or the amine is left unreacted. The order of the addition of the co-reactants is not generally important and these can be added either at ambient temperature or at reaction temperature. For example, the reactants may be charged in increments to a suitable reaction vessel equipped with a mechanical stirrer, a thermometer, a Dean-Stark adapter or other water collector and a nitrogen inlet. The vessel containing the reactants is heated under a blanket of nitrogen. The reaction may be carried out under atmospheric pressure or under vacuum. The reaction temperature to be used in the synthesis may be varied, but preferably ranges from ambient temperature to 300xc2x0 C. under normal pressure. More preferably, the temperature ranges from ambient to 250xc2x0 C., and most preferably from 120 to 220xc2x0 C. Water is removed as condensate as the reaction progresses. After the completion of the reaction, the additive is cooled to 140-150xc2x0 C. and discharged into a release box and allowed to cool overnight. The product is then cooled with liquid nitrogen, dried and ground cryogenically to a fine powder using a Brinkmann centrifugal mill.
The rheological additives used in the present invention may be synthesized with or without a catalyst. The catalyst, if used, may be selected from those, which are normally used for condensation reactions. Examples of such catalysts include, but are not limited to, sulfuric acid, orthophosphoric acid, p-toluene sulfonic acid, dibutytin dilaurate, tetraalkyl tin or titanium compounds, metal hydrides and the like. A preferred catalyst is orthophosphoric acid. The catalyst should generally be used in an amount of from about 0.001 to 2.5 percent by weight based on the total weight of the reactants.
Inventive paints and coatings can be prepared using present standard and diverse paint and coatings base formulations by merely replacing existing Theological additives with the inventive additives described above. Amounts of additives used are normally between 0.5 to 3.5% of the base formulation. Alkyd enamel paints, air drying alkyd paints, long oil alkyd baking paints, two-pack epoxy polyamide primer paints and pvc topcoats are preferred paint coating systems.